1. Field of the Invention
The present invention relates to a television receiver having the teletext receiving function, i.e., a function of displaying teletext pictures corresponding to teletext signals superimposed in the vertical blanking period of television signals. The present invention also relates to a method for superimposing a teletext picture on a television picture.
2. Description of the Related Art
A character broadcasting system generally referred to as a teletext is currently available. According to this character broadcasting system, a television (TV) broadcasting station superimposes coded character data on a TV signal during a predetermined horizontal scanning period of a vertical blanking period of the TV signal and transmits the coded character data together with the TV signal. A TV signal receiving station (i.e., a TV receiver) picks up the coded character data and decodes it into original character data for viewing on the TV screen.
A TV broadcasting station transmits a plurality of character broadcast programs by superimposing them in a plurality of horizontal scanning periods of the TV signal. Therefore, a user or viewer first selects the channel through which the character broadcast program he or she wants to view is transmitted by operating key input means, such as a remote control hand set, and then designates the program number corresponding to the character broadcast program by operating the key input means, thereby viewing on the TV screen a teletext picture corresponding to the character broadcast program.
However, in a conventional TV receiver having a teletext receiving function, which allows the above teletext picture to be displayed on the TV screen, the TV display mode must be first switched to the teletext display mode, so as to monitor the character broadcast program. Therefore, when the user is viewing the teletext picture, he or she cannot know what information is displayed on the TV picture. Conversely, when the user is viewing the TV picture, he or she cannot know the information displayed on the teletext picture. In the conventional TV receiver, therefore, the teletext picture cannot be displayed on the TV screen without switching the mode from the TV display mode to the teletext display mode; the conventional TV receiver does not permit the user to view both the teletext picture and the ordinary TV picture at the same time.